gone is their energy and playfulness. researchers have mixed and the depressants in with their food. after a few weeks, the staff noticed a change. >> that would just sit in the corner and do nothing. after the invention, they are playing with each other and interacting and doing much better now. >> this chimp used to scream all the time in terror. now his main worry is someone might take his ^. these two now play affectionately. hundreds up chimps have been used in experiments over the years. many windup traumatized. 20 years ago, chimp research was at its side, particularly in the u.s. but then they were needed for hiv research. because the public opposition, their use is not decreasing. a recent scientific committee has recommended that more than 300 chimps should be retired in about their remaining years at a sanctuary. simply releasing a chimps will not be enough. many 1 non--- many may well need anti-depressant. >> i think, yes, there is a sizable amount of chimps that could potentially benefit from this sort of a t